This invention concerns surface cleaning systems, and more particularly concerns the liquid cleaning solutions cycled within such systems, especially systems of the continuous flow recycling type.
Continuous flow recycling has gained widespread acceptance as an effective technique for cleaning carpets, upholstery, fabric, wall coverings and hard surfaces. Such systems spray a liquid cleaning solution toward a surface being cleaned. Simultaneously, a vacuum source creates a high velocity air stream that draws the atomized liquid toward the surface, and into the material beneath the surface in the case of porous material. Almost immediately, the air stream is diverted to draw the liquid upwardly away from the surface, along with soil and other contaminants extracted from the surface and/or from porous material beneath the surface. This enables the recovery of most of the cleaning solution, for filtration and recycling to extract further foreign matter from the surface being cleaned.
Continuous flow recycling systems typically include a tank or canister containing liquid cleaning solution, a motor and a pump for circulating the cleaning solution, a cleaning tool head for direct spray application of the liquid to a surface being cleaned, and a vacuum motor and blower for recovering the liquid solution and returning it from the cleaning tool head to the tank. These components may be separate and connected through tubing or hosing, or disposed within the housing of a self-contained unit to which a cleaning tool head is mounted directly, as shown in U.S. Pat. No. 5,432,975 (Hilmanowski).
Continuous flow recycling systems, and other systems that cycle liquid solution (e.g., from a supply tank to a separate tank for receiving spent liquid), have been found effective in suspending and removing soil. There are certain contaminants, however, that are difficult to control with ordinary aqueous cleaning solutions. For example, carpets and upholstery fabric, particularly in warm and humid environments, provide breeding grounds for microorganisms. This problem is a particular concern in hospitals, clinics and other treatment and diagnostic facilities. In these cases, the conventional cleaning solutions can be augmented with additives such as quaternary ammonium compounds, chlorine, or acidic sanitizers. Each of these additives has disadvantages. The quaternary compounds have only a limited effect on gram-positive bacteria and tend to leave a residue that attracts soil to the surface just cleaned. Chlorine compounds are not effective in high soil load conditions, are corrosive to metals and certain other materials, can bleach dyes, and can degrade natural fibers such as wool and cotton. Finally, acidic sanitizers are not particularly effective against yeasts and molds, and have a residual acidity that may promote the growth of certain yeasts and molds. Further, all of these additives are potential pollutants that raise problems of waste disposal.
Use of these additives in continuous flow recycling systems raises a further problem of accumulation of the microbiological organisms and other contaminants that are not effectively reduced in concentration or eliminated by the additive being used. This particular problem can be avoided by using a system that does not recycle the liquid cleaning solution. However, systems that do not recycle the solution require frequent replenishment of the cleaning solution and waste disposal of the recovered solution.
Liquid cleaning solutions incorporating surfactants are known. For example, U.S. Pat. No. 5,338,475 (Corey, et al.) discloses a carpet cleaning composition including hydrogen peroxide and a nonionic, anionic or amphoteric surfactant from about 0.05-5.0%, by weight, advising the selection of a surfactant that, when employed in the recommended concentrations, does not leave a tacky or oily residue.
U.S. Pat. No. 4,490,270 (Hackett, et al.) is directed to a sanitizing liquid shampoo for carpets, including 0.1-20% surfactant, by weight. Suggested surfactants include sodium lauryl sulfate and sodium lauryl ether sulfate. U.S. Pat. No. 5,284,597 (Rees) teaches stable aqueous soft surface cleaning compositions containing a peroxygen reagent and an anionic surfactant such as sodium lauryl sulfate which can concentrate 0.4 to 0.6 percent of a base composition.
U.S. Pat. No. 5,492,540 (Leifheit, et al.) discloses a soft surface cleaning composition including from about 0.2% to about 6.0% of a surfactant, by weight. Leifheit teaches using surfactants for which the final composition dries to a non-tacky or non-sticky residue, to reduce the likelihood of resoiling fibers after their initial cleaning.
U.S. patent application Ser. No. 08/659,393 (Berglund), entitled Continuous Flow Cleaning System With Ozone Injection and filed Jun. 6, 1996 (incorporated herein by reference), discloses the incorporation of an ozone generator within continuous flow recycling systems and other systems that cycle liquid cleaning solutions. The incorporation of ozone (O.sub.3) into the liquid cleaning solution provides several advantages:
1. The liquid cleaning solution is effective against contaminants resistant to ordinary cleaning solutions, yet avoids formation of unwanted residues, waste disposal problems and corrosion or other damage to materials being cleaned; PA1 2. Ozone can be introduced into the cleaning liquid solution in a manner that enhances sanitizing effectiveness of the solution and tends to sanitize and deodorize the air near where the cleaning solution is contained and applied; and PA1 3. The cleaning solution more effectively degrades organic soils and sanitizes treated surfaces, and more effectively maintains the fluid cycling equipment in a cleaner, more sanitized condition. PA1 (a) providing a liquid surface cleaning composition consisting essentially of water and a surfactant at a concentration from about 10 ppm to about 200 ppm, by weight, wherein the surfactant is resistant to interacting or combining with ozone; PA1 (b) incorporating ozone into the liquid cleaning composition; PA1 (c) delivering the ozone-containing cleaning composition to an application area of a surface to be cleaned; and PA1 (d) providing a vacuum to draw the cleaning compsition, air and removed soil away from the application area.
Preferably, ozone is introduced into the liquid cleaning solution in a gaseous state. Some of the ozone is dissolved, while some of the ozone remains in the gaseous state. In either case, the ozone is a powerful oxidizing agent and an effective biocide at low concentrations, e.g., in the range of about 0.01 to about 4 ppm (parts per million). Ozone is more water soluble than oxygen, so that it readily combines with any water-based cleaning solution. Concentrations in air or water diminish due to the transient nature of ozone (approximately a 20-minute half-life). Consequently, ozone leaves no residue to attract contaminants to surfaces just cleaned. The decomposition of ozone produces oxygen, avoiding any concerns of toxicity, pollution or waste disposal. At low concentration levels, ozone is non-corrosive and does not discolor or otherwise degrade carpeting or fabric.
The presence of ozone is beneficial throughout the cleaning system, not just at the cleaning tool head. In the solution recovery segment, ozone continues to work on soils which have been extracted from the surface, and tends to sanitize and maintain the cleanliness of the hosing forming the recovery segment.
Ozone dissolved within the cleaning solution in the tank continues to work on soils returned to the tank from the application area. Some of the ozone escapes from the cleaning solution in the tank and interacts with air in the cavity above the cleaning solution. This combines with undissolved gaseous ozone returned to the cavity via the recovery segment, to provide cleaner and more sanitized air within the tank.
Thus, the escape of ozone from the cleaning solution, sometimes referred to as "outgasing," has a known beneficial effect.
At the same time, the outgasing of ozone has several undesirable consequences. One of these is that outgasing reduces the concentration of dissolved ozone within the liquid cleaning solution. The reduction of ozone concentration within the cleaning solution eventually reduces the effectiveness of the cleaning solution. Ozone concentrations are further reduced by cleaning solution additives that have a high affinity for oxidation, or otherwise promote decomposition of ozone.
Another unwanted consequence of outgasing is that it can increase the amount of ozone released to the atmosphere around the system, primarily through an air exhaust of the tank or canister. As disclosed in the aforementioned application, Ser. No. 08/659,393, a bed of activated carbon, that catalytically converts excess ozone into oxygen, can be provided at the canister exhaust to reduce the concentration of ozone at the exhaust ports.
The above notwithstanding, it is preferred to reduce the decomposition and outgasing of ozone as much as possible, both to maintain the effectiveness of the liquid cleaning solution and to minimize the ozone released by the system into the surrounding atmosphere.
Accordingly, it is an object of the present invention to provide a liquid cleaning solution incorporating constituents that inhibit ozone decomposition.
Another object is to provide a liquid cleaning solution in which the tendency of ozone outgasing is reduced.
A further object is to provide a fluid cycling cleaning system in which a liquid surface cleaning composition contained within and circulated throughout the system includes constituents resistant to interacting or combining with ozone.
Yet another object is to provide a process for cleaning a surface with a liquid cleaning solution that incorporates ozone and components resistant to combining or interacting with ozone.